Re: [net-next 14/14] ptp: xgbe: convert to .adjfine and adjust_by_scaled_ppm

[Tom Lendacky <thomas.lendacky@amd.com>]

On 8/19/22 16:04, Keller, Jacob E wrote:
>> -----Original Message-----
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>> Sent: Friday, August 19, 2022 9:05 AM
>> To: Keller, Jacob E <jacob.e.keller@intel.com>; netdev@vger.kernel.org
>> Cc: K. Y. Srinivasan <kys@microsoft.com>; Haiyang Zhang
>> <haiyangz@microsoft.com>; Stephen Hemminger <sthemmin@microsoft.com>;
>> Wei Liu <wei.liu@kernel.org>; Cui, Dexuan <decui@microsoft.com>; Shyam
>> Sundar S K <Shyam-sundar.S-k@amd.com>; David S. Miller
>> <davem@davemloft.net>; Eric Dumazet <edumazet@google.com>; Jakub Kicinski
>> <kuba@kernel.org>; Paolo Abeni <pabeni@redhat.com>; Siva Reddy Kallam
>> <siva.kallam@broadcom.com>; Prashant Sreedharan
>> <prashant@broadcom.com>; Michael Chan <mchan@broadcom.com>; Yisen
>> Zhuang <yisen.zhuang@huawei.com>; Salil Mehta <salil.mehta@huawei.com>;
>> Brandeburg, Jesse <jesse.brandeburg@intel.com>; Nguyen, Anthony L
>> <anthony.l.nguyen@intel.com>; Tariq Toukan <tariqt@nvidia.com>; Saeed
>> Mahameed <saeedm@nvidia.com>; Leon Romanovsky <leon@kernel.org>;
>> Bryan Whitehead <bryan.whitehead@microchip.com>; Sergey Shtylyov
>> <s.shtylyov@omp.ru>; Giuseppe Cavallaro <peppe.cavallaro@st.com>;
>> Alexandre Torgue <alexandre.torgue@foss.st.com>; Jose Abreu
>> <joabreu@synopsys.com>; Maxime Coquelin <mcoquelin.stm32@gmail.com>;
>> Richard Cochran <richardcochran@gmail.com>; Thampi, Vivek
>> <vithampi@vmware.com>; VMware PV-Drivers Reviewers <pv-
>> drivers@vmware.com>; Jie Wang <wangjie125@huawei.com>; Guangbin Huang
>> <huangguangbin2@huawei.com>; Eran Ben Elisha <eranbe@nvidia.com>; Aya
>> Levin <ayal@nvidia.com>; Cai Huoqing <cai.huoqing@linux.dev>; Biju Das
>> <biju.das.jz@bp.renesas.com>; Lad Prabhakar <prabhakar.mahadev-
>> lad.rj@bp.renesas.com>; Phil Edworthy <phil.edworthy@renesas.com>; Jiasheng
>> Jiang <jiasheng@iscas.ac.cn>; Gustavo A. R. Silva <gustavoars@kernel.org>; Linus
>> Walleij <linus.walleij@linaro.org>; Wan Jiabing <wanjiabing@vivo.com>; Lv Ruyi
>> <lv.ruyi@zte.com.cn>; Arnd Bergmann <arnd@arndb.de>
>> Subject: Re: [net-next 14/14] ptp: xgbe: convert to .adjfine and
>> adjust_by_scaled_ppm
>>
>> On 8/18/22 17:27, Jacob Keller wrote:
>>> The xgbe implementation of .adjfreq is implemented in terms of a
>>> straight forward "base * ppb / 1 billion" calculation.
>>>
>>> Convert this driver to .adjfine and use adjust_by_scaled_ppm to calculate
>>> the new addend value.
>>>
>>> Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
>>> Cc: Tom Lendacky <thomas.lendacky@amd.com>
>>> Cc: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
>>> ---
>>>
>>> I do not have this hardware, and have only compile tested the change.
>>>
>>>    drivers/net/ethernet/amd/xgbe/xgbe-ptp.c | 20 ++++----------------
>>>    1 file changed, 4 insertions(+), 16 deletions(-)
>>>
>>> diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-ptp.c
>> b/drivers/net/ethernet/amd/xgbe/xgbe-ptp.c
>>> index d06d260cf1e2..7051bd7cf6dc 100644
>>> --- a/drivers/net/ethernet/amd/xgbe/xgbe-ptp.c
>>> +++ b/drivers/net/ethernet/amd/xgbe/xgbe-ptp.c
>>> @@ -134,27 +134,15 @@ static u64 xgbe_cc_read(const struct cyclecounter
>> *cc)
>>>    	return nsec;
>>>    }
>>>
>>> -static int xgbe_adjfreq(struct ptp_clock_info *info, s32 delta)
>>> +static int xgbe_adjfine(struct ptp_clock_info *info, long scaled_ppm)
>>>    {
>>>    	struct xgbe_prv_data *pdata = container_of(info,
>>>    						   struct xgbe_prv_data,
>>>    						   ptp_clock_info);
>>>    	unsigned long flags;
>>> -	u64 adjust;
>>> -	u32 addend, diff;
>>> -	unsigned int neg_adjust = 0;
>>> +	u64 addend;
>>>
>>> -	if (delta < 0) {
>>> -		neg_adjust = 1;
>>> -		delta = -delta;
>>> -	}
>>> -
>>> -	adjust = pdata->tstamp_addend;
>>> -	adjust *= delta;
>>> -	diff = div_u64(adjust, 1000000000UL);
>>> -
>>> -	addend = (neg_adjust) ? pdata->tstamp_addend - diff :
>>> -				pdata->tstamp_addend + diff;
>>> +	addend = adjust_by_scaled_ppm(pdata->tstamp_addend, scaled_ppm);
>>
>> Since addend is now a u64, but the called function just afterwards,
>> xgbe_update_tstamp_addend(), expects an unsigned int, won't this generate
>> a compiler warning depending on the flags used?
>>
> 
> It doesn't seem to generate anything with W=1 or W=2 on my system. Its possible that the compiler can deduce that this won't overflow a u32?
> 
> We could add a check to ensure it doesn't overflow the u32 size?

As long as we don't see a warning, I'm ok with it.

Acked-by: Tom Lendacky <thomas.lendacky@amd.com>

Thanks,
Tom

> 
>> Thanks,
>> Tom
>>
>>>
>>>    	spin_lock_irqsave(&pdata->tstamp_lock, flags);
>>>
>>> @@ -235,7 +223,7 @@ void xgbe_ptp_register(struct xgbe_prv_data *pdata)
>>>    		 netdev_name(pdata->netdev));
>>>    	info->owner = THIS_MODULE;
>>>    	info->max_adj = pdata->ptpclk_rate;
>>> -	info->adjfreq = xgbe_adjfreq;
>>> +	info->adjfine = xgbe_adjfine;
>>>    	info->adjtime = xgbe_adjtime;
>>>    	info->gettime64 = xgbe_gettime;
>>>    	info->settime64 = xgbe_settime;